New methods of delivering large macromolecules (proteins and peptides) continue to be sought. One of the avenues investigated concerns the use of membrane-mimetic amphiphiles. A study of membrane-mimetic amphiphiles extends back to the first decade of the 20th century. Experiments using physical and chemical methods have shown that such molecules assume preferred arrays in the presence of water. Formation of these arrays, which includes micelles, monolayers and bimolecular layers is driven by the need of the polar head groups, which may be ionogenic or not, to associate with water, and the need of the polar hydrophobic tails to be excluded from water, (Small, D; Handbook of Lipid Research, vol. 4, 1986; Tanford, J: The Hydrophobic Effect, John Wiley & Sons, 1980; Fendler, J. Membrane Chemistry, 1982). Exactly which type of structure is assumed depends on upon the nature of the amphiphile, its concentration, the presence of other amphiphiles, temperature and the presence of salts and other solutes in the aqueous phase.
Membrane-mimetic amphiphiles include molecules that are insoluble in water but can take up water, and molecules that have appreciable solubility in water under limiting conditions. The former amphiphiles do not form molecularly disperse solutions in water but may swell considerably with water to form lamellar phases. The latter amphiphiles can, at some temperatures, form solutions of dispersed monomers in water and often undergo the following sequence as the concentration in water is increased: monomeric solution to micellar solution. The manufacture of non-phospholipid liposomes, depends on the manipulation of environmental variables (e.g. temperature, hydration and composition) in an appropriate temporal sequence so as to cause non-phospholipid amphiphiles to form liposomal structures.
Gebicki et al. (Nature, 243, 232, 1973: Chem. Phys. Lipids, 16, 142, 1976; Biochem. Biophys. Res. Commun. 80, 704, 1978; Biochemistry, 17, 3759, 1978) demonstrated the formation of water containing vesicles enclosed by oleic acid. Others, as disclosed for example in U.S. Pat. Nos. 4,772,471 and 4,830,857, and in J. Microencapsul. 4, 321, 1987, have made lipid vesicles from single tailed ether or esters derivatives of polyglycerol. These liposomes were found suitable for cosmetic products. Murakami et al (J. Am. Chem. Soc, 101, 4030, 1979; J. Am Oil Chem Soc. 66, 599, 1989) formed single compartment vesicles with one or more bilayer walls composed of cationic amphiphiles involving amino acid residues. Kaler et al (Science, 245, 1371, 1989) demonstrated that appropriate aqueous mixtures of single-tailed cationic and anionic surfactants spontaneously form single-walled vesicles, presumably via salt formation. Others have developed methods for manufacture of paucilamellar, non-phospholipid liposomes that can be formed from a variety of amphiphiles as well as from certain phospholipids. The liposomes have two or more membranes surrounding an amorphous core, each membrane being composed of amphiphile molecules in bilayer array. The core accounts for most of the vesicle volume and encapsulating substances.
The above-mentioned non-phospholipid based liposomes are mainly used for the delivery of moisturizers and cosmetic ingredients used topically or externally as creams or moisturizers. In some cases such liposomes may be used as an ointment for delivery of some pharmaceutical products. Many ingredients utilized in the above products have been found to be inadmissible in the human body and are not approved by the regulatory agencies around the world for the purpose of oral administration and as a vehicle for delivery of macromolecules (proteins and peptides) as life saving therapeutics. Furthermore, other non-phospholipid based liposomes have been developed for non-pharmaceutical applications, e.g. water-borne oil paints, surface cleansers, heavy duty industrial cleansers and skin-cleansing detergents.
Certain aspects of the present invention aims at the development of oral compositions consisting of mixture of certain non-phospholipid based membrane-mimetic amphiphiles (suitable and approved by the regulating agencies for oral formulation of human pharmaceutical products) in combination of specific phospholipids to form multilamellar liposomes which are very stable and are smaller than the pores of the gastrointestinal (GI) tract.
Relatively very little progress has been made in reaching the target of safe and effective oral formulations for peptides and proteins. The major barriers to developing oral formulations for proteins and peptides include poor intrinsic permeability, lumenal and cellular enzymatic degradation, rapid clearance, and chemical stability in the GI tract. Pharmaceutical approaches to address these barriers, which have been successful with traditional small, organic drug molecules, have not readily translated into effective peptide and protein formulations. Although the challenges are significant, the potential therapeutic benefits remain high especially in the field of diabetes treatment using insulin.
Researchers have explored various administration routes other than injection for proteins and peptides. These routes include administration through oral, intranasal, rectal, vaginal cavities for the effective delivery of large molecules. Out of the above four mentioned routes oral and nasal cavities have been of greatest interest. Both the oral and nasal membranes offer advantages over other routes of administration. For example, drugs administered through these membranes have a rapid onset of action, provide therapeutic plasma levels, avoid a first pass effect of hepatic metabolism, and avoid exposure of the drug to a hostile GI environment. Additional advantages include easy access to the membrane sites so that the drug can be applied, localized and removed easily. Further, there is a good potential for prolonged delivery of large molecules through these membranes.
The oral routes have received far more attention than have the other routes. The sublingual mucosa includes the membrane of ventral surface of the tongue and the floor of the mouth whereas the buccal mucosa constitutes the lining of the cheek. The sublingual mucosa is relatively permeable thus giving rapid absorption and acceptable bioavailability of many drugs. Further, the sublingual mucosa is convenient, acceptable and easily accessible. This route has been investigated clinically for the delivery of a substantial number of drugs.
Various mechanisms of action of penetration of large molecules using enhancers have been proposed. These mechanisms of action, at least for protein and peptidic drugs include (1) reducing viscosity and/or elasticity of mucous layer, (2) facilitating transcellular transport by increasing the fluidity of the lipid bilayer of membranes, (3) facilitating paracellular transport by altering tight junction across the epithelial cell layer, (4) overcoming enzymatic barriers, and (5) increasing the thermodynamic activity of drugs (Critical Rev. 117-125, 1992).
Many penetration enhancers have been tested so far and some have been found effective in facilitating mucosal administration of large molecular drugs. However, hardly any penetration enhancing products have reached the market place. Reasons for this include lack of a satisfactory safety profile respecting irritation, lowering of the barrier function, and impairment of the mucocilliary clearance protective mechanism. It has been found that some of the popular penetration enhancers, especially those related to bile salts, and some protein solubilizing agents, impart an extremely bitter and unpleasant taste. This makes their use impossible for human consumption on a day to day basis. Several approaches were utilized to improve the taste of the bile salts based delivery systems, but none of them are commercially acceptable for human consumption to date. Approaches utilized include patches for buccal mucosa, bilayer tablets, controlled release tablets, liposome formulations, use of protease inhibitors, bucally administered film patch devices, and various polymer matrices. Further the problem is compounded because of the localized side effect of a patch which often results in severe tissue damage in the mouth.